44 LEAVES. 



b. Some plants are destitute of leaves ; they are then called Aphyllous, from 

 the Greek a, to "want, phyllov, a leaf 



c. Specific names are often given from some circumstance of the leaf: the Hepati- 

 CA triloba is that species of the Hepatica which has leaves with three divisions, called 

 lobes. The VIOLA rotundifolia, is a species of violet with round leaves. A knowl- 

 edge of the various appearances presented by leaves is of great importance to the 

 botanical student ; in order to become acquainted with these, much practice in the 

 analysis of plants is necessary. Engravings will assist the pupil in understanding 

 definitions, but Nature should ever be consulted when practicable. 



52. The new plant is called ^^jpliyton; in its simplest form it 

 consists of two leaves and a bud, which is the axis, and forms 

 the stem and root. Seminal leaves first appear above the sur- 

 face of the earth, as in the garden bean ; these leaves are the 

 cotyledons, which, after nom-ishing the phyton, decay. Pri- 

 mordial leaves appear in the axils of the seminal leaves, and re- 

 semble them in position, form, and size. The primordial leaf, 

 according to the fanciful idea of a French botanist, is a sketch 

 which nature makes before the perfection of her work. Char- 

 acteristic leaves are found in the matm'e state of the plant. 

 According to the idea above advanced, nature here perfects 

 her design. It is not always, however, that this process, with 

 regard to change of leaves, takes place ; as in many cases, the 

 proper, or characteristic leaf, is the only one which appears. 



53. Venation of Leaves. — ^The expanded part of the leaf is 

 called the lamina or blade ; the end of the blade next the stem 

 is the hase^ the opposite end the ajyex. llie parencliyma is the 

 cellular tissue which composes the body of the leaf, or the fill- 

 ing of a frame-work or skeleton composed of vasculciT tissue. 

 The bundle of vessels which compose this frame-work are called 

 veins.) sometimes rihs and nerves. The midrib is the principal 

 vein which passes from the leaf-stalk through the center of the 

 leaf; its branches vlyq primary veins, which, when subdivided, 

 are called secondary veins, and a still more minute division, 

 veinlets. The distribution of veins in the leaves is called vena- 

 tion^ sometimes nei'vation. Li succulent plants the veins are 

 sometimes obscure ; these are called liidden-veined. Leaves 

 may be divided into tlm^ee great classes according to their 

 venation. Reticidate or netted leaves, in which the petiole is 

 prolonged into the leaf in the corm of the midrib, and there is 

 an angular net-work of vessels, as occurs in the leaves of ex- 

 ogenous plants, as the oak, rose, &c. Parallel-^ eined.^ in which 

 the veins run in a straight or curved manner from base to apex, 

 or from the midrib to the margin of the leaf, and are connected 

 by simple transverse veins, as a^^pears in most endogenous or 

 monocotyledonous plants, as the lily, grasses, &c. Porhed- 

 veined.) when the veins divide and subdivide by forked divi- 



h. Aphyllous plants — e. Leaves furnish specific characters. — 52. Leaves with respect to succession. — 

 53. Venation of leaves — Reticulate-veined — Parallel-veined — Forked-veined — Feather, and radia^a- 

 veined. 



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